1. Field of the Invention
The present invention relates, in general, to a refrigerating device. More particularly, the invention relates to a temperature controller and method of controlling temperature in a refrigerating device, and is preferably used in conjunction with a refrigerator.
2. Description of the Prior Art
It is known that a temperature controller of a refrigerating device comprises a sensor circuit and a refrigerating cycle driving device. The sensor circuit outputs a temperature signal obtained frm the voltage division point of a voltage divider circuit comprising a temperature sensor and a resistor. The refrigerating cycle driving device controls operation of the refrigerating cycle to cool an inside, for example, of a refrigerator, in accordance with the voltage value of the temperature signal.
The temperature sensor for detecting the internal temperature of the refrigerator consists of, for example, a thermistor whose resistance value has a negative temperature characteristic. In the voltage divider circuit, D.C. power is connected to the temperature sensor and the resistor connected in series. An example of such a temperature controller for a refrigerating device is disclosed in Japanese Utility - Model Laid-Open Publication No. 56-148579, filed on Apr. 17, 1980 in the name of Yasuhiro Ogita.
In Japanese Utility-Model Laid-Open Publication No. 56-148579, the sensor circuit outputs, through a comparator, the temperature signal obtained from the voltage division point of the voltage divider circuit comprising the temperature sensor and the resistor. A microcomputer controls the operation of the refrigerating cycle for cooling the interior of the refrigerator in accordance with the voltage value of the temperature signal.
In general, there is a possibility for the temperature sensor to be subject to failures, such as a disconnection failure or a continuity failure. In the conventional temperature control circuit, when a disconnection failure occurs in the temperature sensor, the voltage of the temperature signal becomes 0. Accordingly, the refrigerating cycle driving device, such as, e.g., a microcomputer, judges that the temperature inside the refrigerator is extremely low, even though it may in fact be above the set temperature, and therefore does not drive the refrigerating cycle. As a result the temperature inside the refrigerator becomes abnormally high, causing the food stored therein to spoil.
When the continuity failure occurs in the temperature sensor, the voltage of the temperature signal becomes the same high voltage as the D.C. power source. Accordingly, the refrigerating cycle driving device judges that the temperature inside the refrigerator is extremely high, even though it may in fact be below the set temperature, and therefore continue to drive the refrigerating cycle. As a result, the temperature inside the refrigerator becomes abnormally low, causing the food stored therein to be frozen.